Method of coating the inner wall surface of a hollow body and a hollow bodycoated thereby

ABSTRACT

A method of coating the inner wall surface of a hollow body, the one end side of which is open and comprises there a free perimeter edge. The method involves covering or masking a region of the inner wall surface, applying an electric potential to the pin holder, the applying an electrolyte to the uncovered region of the inner wall surface, said electrolyte containing a coating material that has a low electrical resistance at the transition between the metallic material of the cylindrical wall of the pin holder and the material of another metallic component part.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of coating the inner wall surface of a hollow body, the one end side of which is open and comprises there a perimeter edge. Such hollow bodies are part of an electrical igniter unit for igniting fuels. The fuels may be solid, liquid or gaseous. The essential components of such an igniter unit are at least one igniter pin made of an electrically conductive material, a pin holder comprising a metal ring, that is oversized relative to the igniter pin so as to define, together with said igniter pin, an annular gap as well as an electrically isolating filling material provided within said annular gap. At the one end of the pin holder there is a sealing cap for receiving the fuel (the igniting means). At the other end of the pin holder, there is a plug that is connected to the pin holder in any suitable manner and into which the igniter pin engages during operating, thus establishing an electrically conductive connection. The whole unit is housed in a housing.

The pin holder generally consists of an isolating material such as glass, a plastic, ceramic or glass ceramic material. If the isolating filling material is glass, it has to be sealed to the metal to form a vacuum-tight assembly.

2. Description of the Related Art

Such type ignition units are widely used in the electronics industry and in electrical engineering. The glass used for sealing hereby serves as an insulator. Typical glass-to-metal feedthrough devices have the following structure: metallic inner conductors are sealed within a sintered glass preform, said sintered glass perform being sealed to an outer metal part.

The ignition units mentioned are used for airbags or for belt tighteners in automotive vehicles. The unitary igniter unit, with the pin holder formed as a glass-to-metal feedthrough, includes a bridge wire. The glass-to-metal feedthrough plays an important part therein. It is necessary that the isolated electric voltage generated by one or two metallic pins be reliably provided to a housing.

Known glass-to-metal feedthroughs are realized in the following manner: a pin, which is sealed within glass or isolated, and an additional conductor, which serves as the ground wire, usually are welded or soldered. They thus establish the required connection to the metallic housing. This embodiment is very complicated and expensive to manufacture. A major disadvantage is that the body contact to the outer housing is not very stable. This may have serious consequences, more specifically with regard to their use in air bags or belt tighteners as mentioned herein above by way of example.

Known igniter units of the type mentioned herein above or similar are described in U.S. Pat. No. 6,274,252, U.S. Pat. No. 5,621,183, DE 29 04 174 A1 or DE 19927233A1.

All of the igniter units mentioned comprise two metal pins. The present invention is mainly directed to electrical igniter units comprising but one single pin.

The igniter units described herein above cause serious problems which are, that the transitions between the conductive parts have a relatively high resistance. Another disadvantage of known igniter units is their short durable life. The operational life of known igniter units is unsatisfactory. In part at least, this is due to corrosion of the components involved.

To reduce the electrical resistance at the transition between plug and pin holder, a coating of a material the electrical resistance of which is low is applied in the transition zone. A suited material is gold, for example. Gold is electrolytically deposited onto the inner surface of the hollow body serving as the pin holder and likewise onto the metal pin protruding beyond its glass mount. This avoids corrosion in the transition zone between the pin holder and plug. However, free gold particles have been found wandering around outside of the coating. These wandering particles disturb the sensitive system pin holder/plug and compromise the operation of the igniter unit.

The gold particles mentioned have been defined as having been rubbed off and attempts have been made to improve the bonding performance of the coating by changing the operational parameters of electrolytic deposition. This was not successful, though.

SUMMARY OF THE INVENTION

The invention provides a method by which the inner side of a cylindrical hollow body—more specifically of a pin holder of an igniter unit—can be reliably and durably coated and by which particles will not detach from the coating.

This object is solved by the features of claim 1. A hollow body of the desired type is defined in claim 8.

Using for electrolytic deposition the method mentioned, which involves applying a direct voltage to the hollow body, a relatively strong electrical field forms in the region of its free perimeter edge. As a result thereof, the coating thickness in the edge region is unusually great. The thickness increases toward the edge in such a manner that it virtually forms a bulge in the edge region (when viewed in a longitudinal section through the hollow body). This bulge tends to flake or peel off. These effects have not been recognized hereto before because the particles that are flaking or peeling off are extremely small. The solution, in accordance with the invention, is both simple and successful: the inner wall surface of the hollow body is covered in the region of the free perimeter edge.

This can be accomplished in a number of ways. The simplest is to place an annular screen or an annular mask onto the region of the inner wall surface that is to be covered prior to beginning the plating process.

For this purpose, it is sufficient if the screened and, as a result thereof, coating-free region is very small in the axial direction of the hollow body. For the pin holders required for igniter units a few millimeters or even a few tenths of a millimeter will suffice. As a result, this region remains free from coating with the adjoined region, which can extend as far as the glass filling the gap, being provided with a coating that has a substantially uniform thickness and is suited for operation of the igniter unit.

As used in the present specification, the term cylindrical hollow body includes hollow bodies having a circular cross-section but also such having other cross-sections such as square cross-sections with rounded corners. Also, the cross-section of the hollow body needs not be constant over its length. On the contrary, a relatively wide diameter circular cylinder may be adjoined with a relatively small diameter circular cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a pin holder for an igniter unit; and

FIG. 2 shows equipment for carrying out the method, in accordance with one form of the invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

The pin holder 1 illustrated in FIG. 1 is part of an igniter unit used in a belt tightener. A sealing cap 2 is used for receiving a fuel, which is shown in a sectional view only, is connected to the pin holder 1.

A plug (not shown) is connected to the end of the pin holder 1 that is confronting the sealing cap 2.

The most important component of the pin holder 1 is a metal pin 3. It is embedded in an isolating filling material 4, which is made of glass, in the instant case.

The pin holder includes a carrier portion 1.1 for receiving the metal pin 3 as well as a sleeve 1.2 with an inner wall surface 1.2.1.

The end of the fused portion of the metal pin 3 is electrically conductively connected to the carrier portion 1.1 by means of a bridge 5.

It only matters that the inner wall surface 1.2.1 of the sleeve 1.2 and the free end of the metal pin 3 are coated. In the instant case, the material used for the coating is gold.

In accordance with the invention, the inner wall surface 1.2.1 will not be coated all over. A certain region will remain bare, said region beginning at the free perimeter edge 1.3 of the sleeve 1.2 and extending approximately as far as the free end of the metal pin 3. Variations thereof are possible. However, the very front region of the free perimeter edge 1.3 should remain free of coating material.

Pin holder 1 and metal pin 3 are in a coaxially aligned relationship having a common longitudinal axis 6.

In the instant case, but one single metal pin 3 is provided. More than one pin could also be provided.

With the method of the invention, the coating is electrolytically deposited. The pin holder 1 is hereby appropriately in the same position as shown herein i.e., with the free perimeter edge 1.3 being directed downwards.

The method, in accordance with the invention, operates in the following manner:

First, the inner wall surface 1.2.1 is covered to the desired extent in the region of the free perimeter edge 1.3, i.e., for example as far as the free tip of the metal pin 3, or beyond, towards the isolating filling material 4, or only so as to terminate short of the free tip of the metal pin 3.

Then, an electric potential is applied to the pin holder 1, this potential generally being a direct voltage.

Next, an electrolyte is applied onto the uncovered portion of the inner wall surface 1.2.1 in such a manner that the coating material of concern, which as already mentioned is gold in the instant case, is deposited.

Nozzles (not shown herein) are suitably used for deposition. A one-way nozzle could be used for each pin holder 1. The nozzle's end is directed toward the uncovered region of the inner wall surface 1.2.1 that is to be coated. It could for example revolve about the common longitudinal axis 6 during coating so as to cover the entire extent of the inner wall surface to be coated. A kinematic inversion is also possible with the nozzle being stationary and the pin holder 1 revolving. It would also be possible to utilize two or more nozzles.

FIG. 2 shows equipment for depositing the gold coating mentioned onto the inner wall surface 1.2.1. of the sleeve 1.2.

The equipment includes a rotary table 7, a loading and unloading station 0 and further stations 10 to 70 for cleaning, gold plating and rinsing. A mask 8—see station 0—serves to protect that region of the inner wall surface 1.2.1 that is to remain free from coating material.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

1. A method of manufacturing an igniter unit, including a hollow pin holder (1) the one end side of which is open and comprises wall with a free perimeter edge (1.3), said method involving the following steps: masking a region of the inner wall surface (1.2.1), said region taking departure from the free perimeter edge (1.3) and extending over a certain axial length of the pin holder's (1) wall; applying an electric potential to the pin holder (1); applying an electrolyte to the uncovered region of the inner wall surface (1.2.1), said electrolyte containing a coating material that has a low electrical resistance at the transition between the metallic material of the cylindrical wall (1.2) of the pin holder (1) and the material of another metallic component part.
 2. The method in accordance with claim 1 in which gold is the coating material.
 3. The method in accordance with claim 1 in which the electrolyte is applied by spraying.
 4. The method in accordance with claim 1 in which prior to depositing the electrolyte, the pin holder (1) is brought into a position in which its longitudinal axis (6) is oriented vertically and in which the free perimeter edge (1.3) is located at the bottom.
 5. The method in accordance with claim 1 in which the electrolyte is continuously being supplied to the inner wall surface (1.2.1) of the pin holder (1).
 6. The method in accordance with claim 1 in which the electrolyte is discontinuously being supplied to the inner wall surface (1.2.1) of the pin holder (1).
 7. The method in accordance with claim 1 in which for electroplating, the pin holders (1) are disposed in receiving stations on a rotary table having a vertical axis.
 8. An igniter unit comprising: a pin holder (1) having a cylindrical wall 9 (1.2) and an end side that is open and forms a perimeter edge (1.3), said cylinder wall including an inner wall surface; an electrolytically deposited coating applied to the inner wall surface (1.2.1), said coating being made of a material that has a relatively low electrical resistance at the transition between the material of the wall (1.2) and another component part; and said inner wall surface (1.2.1) comprising a coating-free region that extends from the free perimeter edge (1.3) over a certain axial length of the wall (1.2).
 9. The igniter unit in accordance with claim 8 in which said pin holder (1) carries a metal pin (3) having one end of which is embedded into an isolating filling material (4) which in turn is enclosed by a portion (1.1) of the pin holder (1), said pin in the region of its length that faces the free perimeter edge (1.3) and protrudes from the isolating filling material is coated with the same material as the inner wall surface (1.2.1) of the pin holder (1). 